Conventionally, in order to convey wafers which are material of substrates for semiconductor devices, wafer conveyance robots equipped with a fork-shaped end effector at a tip end of a robotic arm have been used. This end effector is a thin-plate-shaped robotic hand, of which a root part is cantilevered by a wrist of the robotic arm. Thus, the end effector may be bent by its own weight or the weight of the substrate which is placed thereon.
Further, particularly in the wafer conveyance robot, a work space of the end effector may be restricted narrowly and, thus, the end effector may interfere with other objects. In addition, for example, mechanical troubles, such as backlash of gears, elongation of belts, and gear-tooth jumps, may occur in the robotic arm and the end effector. Due to these causes, when vibration and/or an impact are/is applied to the end effector, a level position offset and/or distortion may occur to the end effector.
The end effector which is deformed as described above may not be able to securely convey the wafer. Therefore, it is desirable to detect the deformation of the end effector before starting the conveyance work. Conventionally, a deformation detection work of the end effector accompanied by disassembly of the device was conducted periodically by workers; however, in recent years, various technologies to automatically detect the deformation of the end effector have been proposed.
For example, Patent Document 1 discloses a substrate conveying device provided with an irradiation part which is provided to a tip-end part of a robotic hand and irradiates light in parallel with an extending direction of the robotic hand, and an offset amount detecting part which receives the light and detects an offset between a light-receiving position and a reference position.
For example, Patent Document 2 discloses a robot which is provided with four range-finding sensors at a robotic hand, and is configured to calculate distortion of the robotic hand based on a parallelism obtained by comparing distances from the surface of a level block, which are measured by the range-finding sensors, with reference values.
Moreover, for example, Patent Document 3 discloses a robot which is configured so that an optical sensor disposed just beside a tip-end part of a robotic hand which is located at reference coordinates irradiates detection light to the robotic hand and receives the light, and if an output of the optical sensor is abnormal, the hand is considered to be deformed and the operation of the robot is then stopped.